A major problem for future economies will be to find alternatives sources of fuel and chemical precursors as the natural oil supplies run down, or are at least unable to fully supply demand at low cost. One such potential source of replacements is biomass.
A biofuel may be considered as any fuel, or component(s) which can contribute to a fuel, which is derived from biomass.
Biofuels are intended to provide an alternative to fossil fuels, and may be used as a source of energy, such as in transport fuels or for generating electricity, or for providing heat. Biomass can also be used to make other useful organic chemical products, and eventually it will be highly desirable to be able to make many chemical intermediates, solvents and polymer intermediates from biomass.
Various means of converting biomass to fuels or to useful organic chemical products have been proposed, such as fermentation, gasification and pyrolysis, however such technologies are limited because of a combination of the cost of implementation, limited product range, scale dependence and extensive waste products. Apart from fermentation, many such technologies work best when the initial biomass is dry, and many sources of biomass, particularly algae, are most readily obtained in a highly wet form.
Methods of converting wet biomass to organic chemical products are known. One such technology is high-pressure liquefaction, which occurs in two variants. One is to hydrogenate the biomass directly by heating a slurry of biomass under a pressurized atmosphere of hydrogen in the presence of a catalyst. The alternative is simply to liquefy the biomass by heating a slurry of biomass under pressure, effectively trying to accelerate the process that led to the formation of natural oil reserves. The advantage of the second process is that biomass can be converted to a liquid that is more easily transported to a refinery, where the advantages of scale can be applied, both to the fuel processing, and to the hydrogen production. Direct hydrogenation is only feasible for the smaller scale production from biomass if the product does not need further refining, and that is not usually the case.
The concept of heating biomass in water to transform it to fuel and other organic chemical products has been reported. Thus Catallo and Junk (U.S. Pat. No. 6,180,845) have shown that heating cellulose in water under near-critical to supercritical conditions led to the production of phenol and substituted phenols, substituted benzene derivatives, cyclopentanone and methylated naphthalenes. Reaction of lignin under the same conditions produced various substituted phenols, naphthalenes and indenes and lipids. Highly nitrogenated biomass gave products particularly rich in phenol, toluene, phenylethanone, substituted pyridines and indole.
Previously, it has been reported (I. J. Miller and S. K. Fellows, Catalytic effects during cellulose liquefaction, Fuel, 1985, 64: 1246-1250; and I. J. Miller and E. R. Saunders, Reactions of possible cellulose liquefaction intermediate under high-pressure liquefaction conditions, Fuel, 1987, 66: 123-129) that the heating of cellulosic biomass to 350-375° C. in the presence of phenol and other catalysts produces phenol, and similar compounds as noted above, e.g. cresols, polyhydroxybenzenes, tetralins and indanes. The difference between these processes and the processes described in U.S. Pat. No. 6,180,845 is that in the former processes significant additional hydrogenation occurred without the use of hydrogen. The liquefaction catalysts so used tended to be acidic in nature, the most basic being sodium dihydrogen phosphate, which gives solutions of pH in the vicinity of 6.3. Reasons for the difference in products presumably include the catalytic involvement of phenol in depolymerising the cellulose, thus holding the carbohydrate in the form of phenol glycosides, as well as the general acidity of the process. (See R. J. Ferrier, W. B. Severn, R. H. Furneaux and I. J. Miller, “The products of zinc chloride promoted decomposition of cellulose in aqueous phenol at 350°”, Carbohydr. Res. 1992, 237: 79-86; and R. J. Ferrier, W. B. Severn, R. H. Furneaux and I. J. Miller, “Isotope studies of the transfer of carbon atoms of carbohydrate derivatives into aromatic compounds”, Carbohydr. Res. 1992, 237: 87-94).
Therefore, from previous work it is known that the type of products obtained by liquefying biomass under hydrothermal conditions may be able to be altered by alteration of the conditions and the media in which the liquefaction takes place
While land-based biomass is of obvious interest as a feed material for hydrothermal processing, of particular interest are microalgae. Microalgae are possibly the fastest growing plants on the planet, and therefore offer the greatest yield per unit area, which may be of considerable importance to overcome the problem of getting sufficient raw material from a smaller area to get the economies of scale required for chemical processing.
Microalgae are unusual amongst plants in that they tend to store energy in lipids as opposed to the more usual carbohydrates, and it is possible, by growing microalgae under controlled conditions, to raise the lipid levels of some micro-algae to in excess of 50% by weight (wt. %). However, the use of photo-bioreactors needed to achieve such lipid yields greatly increase the overall capital and operating costs.
Microalgae can be harvested from adventitious sources, such as water treatment systems, however such microalgae generally devote most of their photochemically derived energy to reproduction, which means that the lipid fraction may be relatively low, and the biomass may largely comprise nitrogen-rich materials such as protein and nucleic acids. As noted above, Catallo and Junk report that hydrothermal treatment of nitrogen-rich biomass gave similar products as other biomass, although indole and pyridine were also formed, the latter being a highly valuable solvent.
It is clear that using adventitious microalgae that must be produced anyway, e.g. in sewage treatment ponds, saves considerable expense in not having to grow specific microalgae in special systems or ponds, however such algae do not have the high lipid content of specially grown microalgae. To date, there are very few clearly successful processes that produce and sell economically and in good volume fuels and chemicals from biomass, and seemingly none from adventitious microalgae. Accordingly, a process that would make desirable fuel from such algae with low lipid content would be important.
It is also desirable to find a process that, by using different conditions but conditions not so different that different processing equipment is required, can be used to make different products so as to take advantage of different market changes. The ability to change the direction of chemical reactions requires agents that alter the relative rates of different reaction pathways, which requires catalysts that can carry out different functions.
It is therefore an object of the present invention to provide a method for processing biomass into organic chemical products that may go at least some way towards addressing at least one of the foregoing problems or which will at least provide the public with a useful choice.